In prior art laser scanning systems, a laser beam is reflected from a rotating polygonal or multifaceted mirror to scan an object, such as an original document. The informational content of the document, in the form of light and dark transmissions, is detected by a photosensor, the photosensor generating corresponding electrical signals. The electrical signals may be transmitted to a remote receiver for modulating a laser beam thereat, the modulated laser beam being directed to a recording media, such as unexposed film or a photosensitive medium whereby an output copy of the original document may be printed. Alternately, the light and dark transmissions from the scanned original document may be printed. Alternately, the light and dark transmissions from the scanned original document may be utilized directly to produce a copy of the original on a local basis.
Presently, most prior art laser scanning systems have been limited to producing black and white copies of the scanned original. For example, the non-impact printer disclosed in U.S. Pat. No. 3,864,697 utilizes a helium-neon gas laser as the source of scanning radiation, the output beam thereof having a wavelength of approximately 633 angstroms, corresponding to the red portion of the visible spectrum. The charged photosensitive medium utilized is sensitive to the output beam of the helium-neon laser, the beam selectively discharging the medium to form an electrostatic latent image corresponding to the information to be provided or copied.
U.S. Pat. No. 3,622,690 discloses an electronic color scanner which provides color corrected separation negatives or positives and which utilizes two lasers for emitting radiation having wavelengths corresponding to the blue, green and red region of the visible spectrum. The first laser comprises an argon laser which is capable of emitting blue and green light simultaneously therefrom, the second laser comprising the aforementioned helium-neon gas laser (red light).
An obvious disadvantage in adapting the laser scanning system disclosed in the latter named patent for use as a color copier or printer is the relatively large cost of the argon laser and the additional complexities inherent in a system which utilizes more than one laser for scanning purposes. In this regard, an article by Fuji et al. in the IEEE Journal of Quantum Electronics, March 1975, page 111, discloses the use of a single hollow-cathode type CW laser as a source of white light consisting of red, green and blue spectral lines. However, the suggested "white" laser is, at this time, not commercially available and its use in color scanning apparatus has yet to be demonstrated.
Therefore, a need exists for a simplified and economical laser scanning system which utilizes commercially available lasers and which is capable of producing radiation of the aforementioned three color spectral lines for use in a color copier or printer.